Improve agent input placeholder

packages/app/src/styles/theme.ts

@@ -110,6 +110,7 @@ const lightSemanticColors = {
   surface1: "#fafafa",       // Subtle hover (was zinc-100, now zinc-50)
   surface2: "#f4f4f5",       // Elevated: badges, inputs, sheets (was zinc-200, now zinc-100)
   surface3: "#e4e4e7",       // Highest elevation (was zinc-300, now zinc-200)
+  surface4: "#d4d4d8",       // Extra emphasis (was zinc-400, now zinc-300)
   surfaceSidebar: "#f4f4f5", // Sidebar background (darker than main)
 
   // Text
@@ -180,6 +181,7 @@ const darkSemanticColors = {
   surface1: "#1f1f23",       // Subtle hover
   surface2: "#27272a",       // Elevated: badges, inputs, sheets
   surface3: "#3f3f46",       // Highest elevation
+  surface4: "#52525b",       // Extra emphasis
   surfaceSidebar: "#121216", // Sidebar background (darker than main)
 
   // Text